1. Field of the Invention
The invention relates to a fingerprint identifying system, more particularly to a fingerprint identifying system having an improved identification rate.
2. Description of the Related Art
Referring to FIG. 1, a conventional fingerprint identifying system 1 includes an image-capturing unit 11, a finger press plate 12, a light-diffusion plate 13 disposed between the image-capturing unit 11 and the finger press plate 12, and a plurality of light sources 14 disposed below the light-diffusion plate 13. The finger press plate 12 has a press surface 121 for disposing a finger (A) thereon. The light-diffusion plate 13 guides the light from the light sources 14 so as to serve as a planar light source transmitting light toward the finger press plate 12, and has a through hole 131 in alignment with the image-capturing unit 11. When the light from the light-diffusion plate 13 illuminates the finger (A) disposed on the press surface 121 of the finger press plate 12, the light illuminating the grooves of the finger (A) is reflected from the press surface 121 to the image-capturing unit 11 through total internal reflection, and the light illuminating the ridges of the finger (A) will be absorbed by the finger (A) so as to create a fingerprint image, which is dark where there are ridges and bright where there are grooves.
However, since there is the through hole 131 in the light-diffusion plate 13, the light illuminating the center portion of the finger (A) is less than that illuminating the remainder of the finger (A). Therefore, the center portion of the finger (A) has an unsatisfactory illumination, which results in an unsatisfactory fingerprint identification rate.
Referring to FIG. 2, another conventional fingerprint identifying system 2 includes an image-capturing device 21, a finger press plate 22 disposed above the image-capturing device 21 for disposing a finger (B) thereon, and two light sources (i.e., light-emitting diodes) 23 disposed at two sides of the image-capturing device 21, respectively. Since the light-emitting diodes have characteristics of high brightness, the center portion of the finger has an improved illumination.
However, since the light-emitting diodes have a relatively small light source angle, the illumination on the finger press plate 22 is uneven. Therefore, the identification rate improved by the fingerprint identifying system 2 is limited.